Lets say that the Yozi are plopped into the warp , in both Fantasy,

>>54303942
I don't know if you were expecting any sort of particular answer, but there really isn't one. The power of the yozi's depends on edition, and who knows what sort of shit they could do if freed, and then you have to answer the question of how they interact with the new settings metaphysics, like human emotion giving power and the fact that time travel is impossible in one setting and very possible in another.

>>54304516
Would it help if we narrowed it down some? Lets say 2e, pre return of the Scarlet Empress. They're still imprisoned within Malfeas within the warp, but their demons can enter the material world via normal 40k means (psykers, cultists, warp storms, etc). They have pretty clear domains in most cases, so lets say they are empowered/can claim mortal souls via their acts of their purview/emotion.

>>54304760
That....does a little. In 2e the yozi are probably at their least impressive, since they're basically just giant collections of charms. (1e and 3e have them more powerful because they don't bother detailing them and just say they're beyond most individual PC's) Them being trapped would limit them a bit, but not by to much. The main thing is they would probably become their own 'faction' in a sense, given that hell is supposedly teeming with billions upon billions of demons, so they could go up against any other faction through sheer numbers.
The imperium would hate them because duh. Eldar probably to. The orks would care about as much as they do the regular chaos gods I would imagine, but they might actually like them because they could have theoretically infinite fights with them. Hard to say how the chaos gods would react. They would obviously not be very big fans of new competition, and thats exluding the obvious overlap between some, like ebon dragon and Tzeentch. Also the power levels would shift around with the empowerment from human souls. ED getting strength from all hatred and deceit and betrayal would skyrocket him, but someone like Oramus has no real obvious sources.
I'm not exactly up to date on my fluff, but I'd but second circle demons around the strength of greater demons, and third circle demons beyond even that. Liger for instance could probably trade blows with any given primarch.
Of course the realistic answer is it maintains status quo because GWS would write it that way

>>54303942
Oh I just realized. It would probably end up something more like heavens reach or whatever space opera expansion there was in shards of exalted dream